Glaucoma is a potentially blinding disease that affects millions of people worldwide. Typically, glaucoma is characterized by elevated intraocular pressure. Increased pressure in the eye can cause damage to the optic nerve which can lead to permanent vision loss if left untreated. Consistent reduction of intraocular pressure can slow down or stop the progressive loss of vision associated with glaucoma. In addition, patients are often diagnosed with pre-glaucoma and ocular hypertension when they exhibit symptoms likely to lead to glaucoma, such as somewhat elevated intraocular pressure, but do not yet show indications of optic nerve damage. Treatments for glaucoma, pre-glaucoma and ocular hypertension primarily seek to reduce intraocular pressure.
Increased intraocular pressure is caused by sub-optimal efflux or drainage of fluid (aqueous humor) from the eye. Aqueous humor or fluid is a clear, colorless fluid that is continuously replenished in the eye. Aqueous humor is produced by the ciliary body, and then flows out primarily through the eye's trabecular meshwork. The trabecular meshwork extends circumferentially around the eye at the anterior chamber angle, or drainage angle, which is formed at the intersection between the peripheral iris or iris root, the anterior sclera or scleral spur and the peripheral cornea. The trabecular meshwork feeds outwardly into Schlemm's canal, a narrow circumferential passageway generally surrounding the exterior border of the trabecular meshwork. Schlemm's canal is the eye's primary drainage vessel. Positioned around and radially extending from Schlemm's canal are aqueous veins or collector channels that receive drained fluid. The net drainage or efflux of aqueous humor can be reduced as a result of decreased facility of outflow, decreased outflow through the trabecular meshwork and canal of Schlemm drainage apparatus, increased episcleral venous pressure, or possibly, increased production of aqueous humor. Aqueous humor flow out of the eye can be restricted by blockages or constriction in the trabecular meshwork and/or Schlemm's canal. When such flow is blocked, increased ocular pressure may result. Increased intraocular pressure can lead to the collapse of Schlemm's canal. This, in turn, may result in a dramatic further increase in intraocular pressure and, ultimately, the onset of glaucoma.
Glaucoma, pre-glaucoma and ocular hypertension currently can be treated by reducing intraocular pressure using one or more modalities, including medication, incisional surgery, laser surgery, cryosurgery, and other forms of surgery. In the United States, medications or medical therapy are typically the first lines of therapy. If medical therapy is not sufficiently effective, more invasive surgical treatments may be used. In other countries, such as those with socialized medical systems or with nationalized health care systems, surgery may be the first line of therapy if it is considered a more cost effective treatment.
A standard incisional surgical procedure to reduce intraocular pressure is trabeculectomy, or filtration surgery. This procedure involves creating a new drainage site for aqueous humor. Instead of naturally draining through the trabecular meshwork, a new drainage pathway is created by removing a portion of sclera and trabecular meshwork at the drainage angle. This creates an opening or passage between the anterior chamber and the subconjunctival space that is drained by conjunctival blood vessels and lymphatics. The new opening may be covered with sclera and/or conjuctiva to create a new reservoir called a bleb into which aqueous humor can drain. However, trabeculectomy carries both long and short term risks. These risks include blockage of the surgically-created opening through scarring or other mechanisms, hypotony or abnormally low intraocular pressure, expulsive hemorrhage, hyphema, intraocular infection or endophthalmitis, shallow anterior chamber angle, and others.
Bypass stents are also used to bridge a blocked trabecular meshwork. Stents can be inserted between the anterior chamber of the eye and Schlemm's canal, bypassing the trabecular meshwork. However, it is difficult to consistently and reliably implant a bypass stent from the anterior chamber into Schlemm's canal. The implant procedure is challenging and stents can become clogged and lose functionality over time. Others have inserted tubular elongated cylindrical hollow stents longitudinally into Schlemm's canal. Cylindrical hollow stents can be configured to allow circumferential fluid flow around the canal. These too can lose functionality over time as a result of occlusion or scarring.
Schlemm's canal is small (e.g., approximately 100 microns to 300 microns in cross-sectional diameter) and circular. Therefore, it can be difficult or expensive to design and manufacture hollow tubular stents of appropriate dimensions for use in opening Schlemm's canal. In addition, hollow tubular stents can be prone to failure and collapse or occlusion over time, as has been shown for cardiovascular stents. Hollow tubular stents incorporating thin walls are especially prone to failure. Further, the walls of tubular stents placed lengthwise along Schlemm's canal can have significant surface area contact with the trabecular meshwork and/or the collector channels, which can result in blockage of the meshwork or collector channels, substantially interfering with transmural flow across the walls of Schlemm's canal and into the eye's collector channels, and with transluminal flow across the lumen of Schlemm's canal, thereby preventing restoration of normal eye drainage.
In view of the above, easily manufacturable, minimally invasive devices for effective, long-term reduction in intraocular pressure are desirable. In addition, methods and kits incorporating such devices are desirable.